1. Field of the Invention
The present invention relates to a control apparatus of a parallel hybrid electric vehicle in which an engine, and a motor serving also as a generator are provided and output torques of the engine and the motor are transmitted to a transmission device through a differential device to produce a running driving force from one or both of the engine and the motor.
2. Description of the Prior Art
A prior art control apparatus of a parallel hybrid electric vehicle is described, for example in Japanese Patent Laid Open Publication Hei No. 8-135762.
In this prior art, a starting apparatus is described in which, for example, an output shaft of an engine is connected to a sun gear of a planetary gear mechanism which constitutes a reduction device, an output shaft of a motor which also serves as a generator is connected to a ring gear, and further a direct coupling clutch as a coupling device is interposed between the sun gear and a ring gear thereby to form a parallel hybrid electric vehicle so that a predetermined starting torque is obtained by adding a braking force by the motor to the ring gear at the time of starting the vehicle.
Here, in a control mode at the time of starting in the prior art, as shown in FIG. 29, at a time point t0, the vehicle is stopped and a D range is selected by a selecting lever, and at the same time, the degree of opening of a throttle is at an idling throttle opening degree .theta.idl as shown at (a) in FIG. 29. As result, an engine speed Ne maintains an idling speed Nidl, and further the motor maintains an idling condition as shown at (e) in FIG. 29.
From this condition, when an accel pedal is depressed at a time point t1, a forward clutch of the transmission device is engaged, so that the transmission device enters a forward power transmitting condition, however, since the inertia of the vehicle is transmitted to an output shaft of the transmission device, the rotational speed No of the output shaft is maintained at zero as shown at (c) in FIG. 29
At this time, the motor is rotated in a negative direction, and as shown at (e) in FIG. 29, enters a regenerating condition while generating a braking torque Te1.
On the other hand, the engine speed Ne is set to a target engine speed Ne* by making reference to a target engine speed map on the basis of a throttle opening degree .theta.m at that time so that the target engine speed Ne* becomes constant at a predetermined throttle opening degree or more which is approximated to a stall rotational speed of a torque converter, and as shown at (b) in FIG. 29, the engine speed Ne is controlled to correspond to the target engine speed Ne*.
At this time, the regenerating condition in which the motor as operated as a generator is continued, and the braking torque is generated, and this braking torque is feedback controlled so that the engine speed Ne is maintained at the target engine speed Ne*.
By this feedback control, the output torque is transmitted to the transmission device from a pinion carrier, and the output speed No is gradually increased as shown at (c) in FIG. 29 and the vehicle is started.
Thereafter, at a time point t2, when the rotational speed Nm1 of the motor becomes "0", the motor transits from the regeneration condition to the driving condition as shown at (e) in FIG. 29, and thereafter the motor rotational speed Nm1 is increased while maintaining the engine speed Ne at the target engine speed Ne*, and accordingly the output shaft rotational speed No is also increased.
Then, at a time point t3 when the output shaft rotational speed No reaches an engagement setting value NeL or higher, a clutch signal is outputted and the direct coupling clutch enters a coupling condition. At the same time, the motor enters a non-driving condition and enters an idling condition, and the rotation of the engine output shaft is transmitted to the output shaft as it is.
However, in the prior art control apparatus of parallel hybrid electric vehicle, at the same time that the throttle opening degree is depressed, the target engine speed Ne* is set reference on the throttle opening degree by making reference to a preset target engine speed map, and the engine speed Ne is made to be increased so as to be maintained at the target engine speed Ne*. Consequently, a difference between the rotational speeds of the motor and the engine becomes extremely large, and at the time of coupling the direct coupling clutch upon the output shaft rotational speed No reaches the engagement setting value NeL, the direct coupling clutch is coupled with the large rotational speed difference remained between the engine speed Ne and the motor speed Nm1, and thus, there is an unsolved problem that a large coupling shock occurs.
Furthermore, in order to prevent the coupling shock, when the coupling of the direct coupling clutch is delayed until a speed difference between the engine speed Ne and the motor speed Nm1 becomes zero, another unsolved problem arises that the driving time of the motor becomes long and the necessity of using a motor having a large rating capacity occurs.
Moreover, since there is a need to change both the engine speed and the motor speed at the initial stage of the start of the vehicle, another unsolved problem arises that most of the torque generated by the engine and the motor will be consumed to accelerate the engine and the motor, and the torque to accelerate the vehicle is reduced and the accelerating performance of the vehicle just after the start will be degraded.